Polyaminomethylenephos phonate derivatives

ABSTRACT

In one embodiment, a scale inhibitor comprising at least one polymethylenephosphonate derivative having the following formula: 
                         
wherein n is a number, wherein M is hydrogen or a cation, wherein R 1 , R 2 , and R 3  are each independently selected from the group consisting of CH 2 PO 3 M 2 , CH 2 R 4 , wherein R 4  is CHOHCH 3 , CHOHCH 2 Cl, or CHOHCH 2 OH, (CH 2 ) m SO 3 M, wherein m is 3 or 4, and CH 2 CH 2 R 5 , wherein R 5  is CONH 2 , CHO, COOR 6 , COOX, or CN, wherein R 6  is CH 3  or C 2 H 5 , and wherein X is an alkali metal or ammonium, and wherein at least one of R 1 , R 2 , and R 3  is not CH 2 PO 3 M 2 . In another embodiment, a method for inhibiting scale formation in water, and in still another embodiment, a method for sequestering iron ions in a water systems, each of the methods comprising the step of providing the water with the above described polymethylenephosphonate derivative.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a new class of phosphonates and relatedsalts, the method of preparation of the same and their utilization inthe preparation of water additives to be used in different industrialfields. More specifically, the products and the processes according tothe present invention provide new additives that prevent the segregationof solids from their aqueous solutions or dispersions by acting asprecipitation inhibitors and dispersants.

2. Description of Related Art

Water in its natural state, as found in rivers, lakes and seas, and withthe exeception of rain water, contains a certain quantity of metal ionsand anions of different types and in various proportions, according totheir origins. Such metal ions cause the formation of a precipitate,when water taken from its natural environment is used for industrialpurposes. In industrial processes, water which is normally inequilibrium with the external environment is affected by differentphysical-chemical conditions, and if the concentration of salts underthese new conditions exceeds the solubility product (“supersaturation”),salt precipitation is observed.

Such precipitating salts are generally formed by earth-alkali metals(Ca; Ba; Mg); among them Calcium—mostly as carbonate but also assulfate—is mostly responsible for phenomena of incrustation in severalindustrial water applications.

The incrustation (not only limited to poory soluble salts) is generallycalled “SCALE” by water treatment experts.

Several factors cause supersaturation and thus the precipitation ofaqueous solutions containing calcium carbonate. The CaCO₃/CO₂/H₂O systemis described schematically here in FIG. 1.

Calcium is present in all surface waters in the form of solublebicarbonate (HCO₃ ⁻) due to the absorption of carbon dioxide from theatmosphere. Any modification of such a system leads, in a more or lessmarked way, to precipitation of CaCO₃.

The causes for the precipitation of CaCO₃ can be classified as follows:

1. Concentration of the solution (evaporation of the aqueous phase);

2. Variations of temperature. By heating, the following transformationtakes place:Ca(HCO₃)→CaCO₃+CO₂+H₂O

3. Variations of the pH. An increase in the pH of the system results inthe following transformation:Ca(HCO₃)₂+2OH⁻→CaCO₃+CO₃ ⁻⁻+2H₂O

As far as cooling and/or heat-exchanger circuits are concerned, theincrustation (scale) formation mechanism can be attributed to aprecipitation of salts from supersaturated solutions in the regionsadjacent to the heat exchange surface of the system.

The effects of such uncontrolled precipitation are sometimes disastrous.For example, in cooling systems, where large volumes of water are used,the deposits of CaCO₃ accumulate in large quantity in the pipes, causinga reduction of the thermal exchange capacity and leading to a virtualocclusion of the pipes, making it necessary to remove the deposits byacidic treatment with consequent shutdown of the plant.

Moreover, the formation of a CaCO₃ incrustation facilitates theincorporation of solid particles that cannot be chemically removed (e.g.SiO₂) or the growth of bacteria and algae.

In order to overcome these disadvantages, pretreatments have beenproposed in the prior art that provide for the preventive elimination oflow-solubility salts by ionic exchange, precipitation, or by the use ofsuitable “sequestering agents” and suitable “scale inhibitors”.

Preventive elimination is in most cases not economically acceptablebecause of the large volumes of water involved.

The same can be said for the chelating agents; it is well known thatthese substances form water-soluble complexes with the metal ions withina well defined stoichiometric molar ratio.

The preferred treatment in the prior art involves the use of suitable“scale inhibitors” that take advantage of the so called “ThresholdEffect.” The Threshold Effect was discovered by observing the behaviorof inorganic polyphosphates that prevent the precipitation of the CaCO₃from supersaturated solutions by means of sub-stoichiometricconcentrations (Hatch and Rice, Indust. Eng. Chem., 31, 51–53 (1939);Reitemeier and Buehrer, J. Phys. Chem., 44 (5), 535–536 (1940); Fink andRichardson U.S. Pat. No. 2,358,222; and Hatch, U.S. Pat. No. 2,539,305).

The mechanism by which precipitation is inhibited is not completelyunderstood today, although the absorption of an inhibitor onto thecrystalline surface seems necessarily to be the first step in theinhibition process. The molecules of the inhibitor are attracted on thegrowing crystalline surface by the presence of metal cations such as Ca,Mg, Ba, for which they have a great affinity.

Once the molecules of the inhibitor are adsorbed, such molecules resideon the surface of the crystal, thus disturbing the regularity of itsgrowth.

If all of this happens during the “nucleation” phase, i.e. during thestage in which a certain number of molecules in solution begins toaggregate in order to give rise to a crystal nucleus, the inhibitor candisturb nuclear growth to such an extent as to make the nucleusredissolve.

Such ability, exercised by various polyelectrolytes, is particularlymarked in the case of phosphonates, which moreover combine corrosioninhibition functions with great resistance to hydrolysis.

However, for every operating condition, there is a limit to the molarratio between inhibitor and metal. In fact, by increasing thephosphonate quantity beyond a certain limit, precipitation of insolublecalcium salts of phosphonates is observed; in such “turbidity” zone, thephosphonate is no longer active. The effectiveness of the phosphonatesat various inhibitor/metal ratios is shown schematically in FIG. 2,wherein the x-axis relates to the molar ratio between metal andinhibitor, while the y-axis relates to the turbidity measurednephelometrically.

Furthermore, it is well known that it is necessary to provide for moreeffective recovery cycles of industrial water—above all because of anincreasing use of water resources—in order to reduce both the quantityof water used and the environmental impact of the treatment agents.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a new class of phosphonates, to asimple and economic process for the production of said new class ofphosphonates, and to the use of said phosphonates in water treatmentapplications. Therefore, the main object of the present invention is anew class of phosphonates that can be used for water treatment.

The compounds that form the object of the present invention are thederivatives of polyaminomethylenephosphonates having the followinggeneral formula:

where n is preferably a number between 2 and 15000, most preferablybetween 2 and 50; wherein M is hydrogen or a cation, wherein R₁, R₂, andR₃ are each independently selected from the group consisting ofCH₂PO₃M₂, CH₂R₄, wherein R₄ is CHOHCH₃, CHOHCH₂Cl, or CHOHCH₂OH,(CH₂)_(m)SO₃M, wherein m is 3 or 4, and CH₂CH₂R₅, wherein R₅ is CONH₂,CHO, COOR₆, COOX, or CN, wherein R₆ is CH₃ or C₂H₅, and wherein X is analkali metal or ammonium, and wherein at least one of R₁, R₂, and R₃ isnot CH₂PO₃M₂.

More particularly, the compounds that form the object of the presentinvention are derivatives of polyaminomethylenephosphonates according tothe above mentioned formula, wherein the polyamine chain may be linearor branched, wherein n is an integer or fractional integer which is, oron average is, from about 2 to about 15000, wherein M₂ may be hydrogenor a suitable cation such as alkali metal or ammonium, and wherein eachR group my be the same or different and is independently selected fromthe following classes:

1. CH₂PO₃M₂, wherein M may be hydrogen or a suitable cation such asalkali metal or ammonium;

2. CH₂R, wherein R=CH₂OH; CHOHCH₃; CHOHCH₂Cl; CHOHCH₂OH;

3. (CH₂)_(n)SO₃M, wherein n=3–4, and where M may be hydrogen or asuitable cation such as alkali metal or ammonium;

4. CH₂CH₂R, wherein R=CONH₂, CHO, COOR₁, COOX, CN, where R₁=CH₃÷C₂H₅,and wherein X may be hydrogen or a suitable cation such as alkali metalor ammonium,

with the condition that at least one of substituent R should bedifferent from the methylenephosphonated group (i.e.: other than—CH₂PO₃M₂).

A particular advantage of the class of phosphonates that are the objectof this invention is that such compounds do not show “Turbidity Zone”and are, therefore, to be considered non calcium-sensitive at anyconcentration and temperature tested.

These compounds are also effectives at high pH values (>10).

This is a very important aspect of the invention, since calciumtolerance of the traditional scale inhibitors like HEDP or ATMP quicklyreduces with an increasing of the pH; in particular, this is importanttoday because water treatment processes are carried out at higher pHvalues than in the past. In fact, a higher pH reduces the effects ofcorrosion, which is more marked at lower pH values.

The advantages of the new class of phosphonates that are the object ofthe present invention can be summarised as follows:

1. A threshold effect that is typical of the phosphonates, i.e.inhibition of precipitation from solutions supersaturated with CaCO₃and/or CaSO₄ at sub-stoichiometric concentrations of the inhibitor;

2. Non calcium-sensitivity, because increases in pH and concentration ofcalcium strongly affect the tolerance of the standard phosphonates(HEDP, ATMP, etc.) to calcium, increasing the possibility ofprecipitation of poorly soluble calcium-phosphonate salts.

3. A dispersing effect better than traditional phosphonates. This newclass of phosphonates behaves like acrylic polymers, accting asdispersants and deflocculants, and stabilizing colloidal systems whichremain steadily dispersed for long periods.

4. A corrosion inhibition that is comparable to that of the standardphosphonates.

5. A chelating effect that is comparable to that of the standardphosphonates.

6. A hydrolytic stability that is similar to conventional phosphonates.

As shown in point 3) above, in addition to the threshold effect, theproducts object of the present invention shows a high “dispersingability”. This property becomes evident when the sequestering power isdetermined by the traditional “HAMPSHIRE” method, and by using thismethod it is not possible to identify an end-point during the titrationwith calcium acetate.

This property also suggests a potential application for this new classof phosphonates as deflocculants, to be used in a certain number ofprocesses and applications where this new class of phosphonates can actas a stabilizer for different knds of dispersions like pigments (TiO₂),kaolin and drilling mud, and in the industrial and domestic detergentfield for their ability to disperse dirt particles. From a general pointof view, because of their particular properties, the products accordingto the present invention can be used for:

a reverse osmosis system;

scale removal;

scale prevention and corrosion control;

boiler cleaning;

bottle washing;

hard surface cleaners;

cooling system;

slurry dispersion;

textile processing;

sanitary cleaners;

paints;

secodnary oil recovery;

oil drilling muds;

laundry detergents;

industrial cleaners;

peroxide stabilisation;

metal finishing;

metal cleaners;

geothermal water;

setting retardants for concrete;

pulp & paper bleaching;

car washing;

flash desalination.

An object of the present invention is also a simple and economic processfor the preparation of the phosphonates and their utilization in theabove mentioned fields, particularly as inhibitors of the formation,deposition, and adhesion of incrustations caused by insoluble salts ofalkali-earth metals, in particular Ca⁺⁺ and Mg⁺⁺, on metal surfaces ofaqueous equipment systems (cooling towers, boilers, gas scrubbers, etc.)

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic illustration of a supersaturation cycle.

FIG. 2 is a chart illustration of the effectiveness of phosphonates asnuclear growth inhibitors at various inhibitor/metal ratios.

DETAILED DESCRIPTION OF THE INVENTION

Detailed descriptions of embodiments of the invention are providedherein. It is to be understood, however, that the present invention maybe embodied in various forms. Therefore, the specific details disclosedherein are not to be interpreted as limiting, but rather as arepresentative basis for teaching one skilled in the art how to employthe present invention jn virtually any detail system, structure, ormanner.

More specifically, embodiments of the present invention will now bedescribed with particular reference to the preparation and to the use ofproducts and processes for the preparation and the stabilization ofaqueous dispersions, even though the scope of the invention should notbe limited to such possible applications.

In one embodiment of the invention, polyaminomethylenephosphonatederivatives are prepared by a phosphonomethylation reaction of polyamineor mixtures of polyamines by means of the Mannich reaction illustratedhereunder:

The phosphonomethylation reaction of amines according to Mannich isdescribed in the literature, eg: K. Moedritzer and R. Irani, J. Organic.Chem. 31 (5) 1603–7.

A typical procedure provides for the amine to be slowly added to amixture of a phosphorus-based acid and hydrochloric acid. The reactionmixture thus obtained is heated to reflux with the addition offormaldehyde. The reaction time can vary from 1 to 5 h.

The derivatives of the polyaminomethylenephosphonate in this embodimentare added to the aqueous systems in quantities between 2 and 50 mg/l, inorder to inhibit precipitation, deposition and adhesion of scale,especially of CaCO₃.

Inhibiting the precipitation and formation of deposits includes thethreshold effect, dispersion, solubilization or modification of theprecipitate's morphology. Inhibiting adhesion defines just that scale iseasily removed, e.g. by simple washing/rinsing and not by mechanical orchemical treatment, because the incrustation is not strongly bonded tothe underlying surface.

The term “scale” includes incrustation formed by CaCO₃, CaSO₄, BaSO₄deposits and can be extended in a generalized manner to include alllow-solubility salts of several cations (Mg, Fe, etc.).

The term “aqueous systems” refers to industrial and/or commercialsystems that use water in heat-exchange processes and includes coolingtowers, boilers, desalination systems, gas scrubbers; furthermore,processes of desalination by reverse osmosis (RO) are included.

Of particular importance are systems operating in severe conditions,such as high pH and high concentrations of calcite (CaCO₃). Thepreparation and the application of the polyaminomethylenephosphonatederivatives according to the present embodiment are illustrated in thefollowing examples, which will clarify their applications, but withoutlimiting the scope of the invention.

Example 1

Into a suitable reaction vessel 350-g of triethylenetetramine werecharged; thereafter the reaction mixutre was heated at 90–95° C.

Ethylene oxide was than added stepwise at such a rate that, withexternal cooling applied, the temperature did not exceed 100° C.

211 g of ethylene oxide were added over a period 1½ hours. The resultantproduct was then converted in the phosphonomethylated derivatesaccording to Mannich's reaction.

With the same synthetic path is possible to obtain β hydroxyethylderivates of linear or branched polyamines or a mixture thereof with anappropriate ratio. Other compounds according to the present embodimentcan be prepared according to the above described procedure by usingpropylene oxide instead of ethylene oxide (β hydroxy propyl derivates).

Example 2

Into a suitable reaction vessel 292 g of triethylenetetramine werecharged.

Under stirring conditions, acrylonitrile was than added stepwise at sucha rate that, with external cooling applied, the temperature did notexceed 50° C.

212 g of acrylonitrile were added over a period 2 hours. The resultantproduct was than converted into phosphonomethylated derivates accordingto Mannich's reaction.

With the same synthetic path is possible to obtain β cyanoethylderivates of linear or branched polyamines or mixture thereof with anappropriate ratio.

Example 3

Into a suitable reaction vessel 292 g of triethylenetetramine werecharged.

Under stirring, 488 g of 1,3-propane sultone, dissolved in 1140 g ofmethanol, was added dropwise at a tempearture between 40–50° C. After 2hours, the methanol was removed by evaporation to dryness and theresidue dissolved in water. The resultant product was than convertedinto phosphonomethylated derivates according to Mannich's reaction.

With the same synthetic path is possible to obtain N-(sulfopropane)amino derivatives of linear or branched polyamines or a mixturethereof with an appropriate ratio.

Other compounds according to the present embodiment can be preparedaccording to the above described procedure by using epichlorohydrin orother different oxiranes derivatives instead of 1,3 propane sultone.

Example 4

Into a suitable reaction vessel 234 g of compound of example 1 wereadded to a 70% a phosphorus-based acid solution (478 g) as well as 32%of hydrochloric acid (342 g). The mixture thus obtained was heated toreflux, 340 g of 37% aqueous formaldehyde solution were added dropwisein the course of about 1 hr, and the reaction mixture was kept at thereflux temperature for 1 additional hr. 300 g of volatile substanceswere then removed from the reaction mixture by distillation. The finalproduct obtained was a viscous fluid having an active substance of 50%.Infrated analysis of the product showed the presence ofmethylenephosphonic amine groups, while P³¹ NMR analysis indicated thatat least 90% of the amine groups had been phosphonomethylated. Theimpurities included unreacted phosphorus-based acid, phosphoric acid andother unidentified compounds.

By following the same synthetic method, phosphonometilated derivativesof polyamine may be obtained or a mix of polyamine having an R groupselected from the following class:

1. CH₂PO₃M₂, wherein M may be hydrogen or an suitable cation such asalkali metal or ammonium;

2. CH₂R, wherein R=CH₂OH; CHOHCH₃; CHOHCH₂Cl; CHOHCH₂OH

3. (CH₂)_(n)SO₃M, wherein n=3÷4 where M may be hydrogen or a suitablecation such as alkali metal or ammonium;

4. CH₂CH₂R, wherein R=CONH₂, CHO, COOR₁, COOX, CN, wherein R₁=CH₃÷C₂H₅,and wherein X may be hydrogen or a suitable cation such as alkali metalor ammonium,

wherein preferably at least one or more than one substituent R isdifferent from the methylenephosphonated group.

Example 5

This example is related to the threshold effect on CaCO₃ at pH=10, T=70°C., 100 ppm of CaCO₃

This method describes the procedure for the determination of thethreshold effect, that is, the ability of a dispersing agent, present insubstoichiometric amounts, to inhibit the precipitation of solutionssupersaturated with calcium carbonate in deionized water.

This method measures the efficiency of a dispersant by titration of thecalcium ion remaining in a solution supersaturated with CaCO₃respectively before and after treatment in an oven at 70° C. The greaterthe calcium concentration after the period in the oven, the greater theefficiency of the dispersant in preventing precipitation of the CaCO₃.

Increasing substoichiometric amounts of phosphonate are dissolved insolutions contaning [Ca⁺⁺] and [CO₃ ⁻⁻] obtained by mixing suitableCaCl₂ and Na₂CO₃ solutions.

The precipitation of calcium carbonate is measured by titration of thefiltered solution. The results obtained are summarised in Table 1.

TABLE 1 Operating Conditions: 100 ppm CaCO₃; pH = 10; T = 70° C.; 24 hInhibition % Inhibitor 0.25 ppm 0.5 ppm 1 ppm Example 4 72 97 99 HEDP 7499 100 ATMP 75 99 100 DTPMP 65 85 100 PBTC 90 100 100 wherein: HEDP =Hydroxy-ethylydene-1,1-diphosphonic Acid; ATMP = Amino-trisMethylenephosphonic Acid; DTPMP = Diethylenetriamine penta(methylenephosphonic acid); PBTC = Phosphono Butane tris CarboxylicAcid.

Example 6

This example relates to the CaCO₃ threshold effect at pH=11.5, T=40° C.,400 ppm of CaCO₃

Following the method described in example 5, the following results wereobtained:

TABLE 2 Operating Conditions: 400 ppm CaCO₃; pH = 11.5; T = 40° C.; 24 hInhibition % Inhibitor 40 ppm 80 ppm 200 ppm 400 ppm 450 ppm Example 4 035 90 92 95 ATMP 0 35 40 60 65 DTPMP 0 35 83 80 80 PBTC 0 30 42 92 95

Example 7

This example relates to CaSO₄ threshold effect at pH=7; T=70° C.; 6800ppm of CaSO₄.

Following the method described in example 5, the solution of CaSO₄ wasprepared starting from CaCl₂ and Na₂SO₄. The results obtained aresummarized hereunder:

TABLE 3 Operating Conditions: 6800 ppm CaSO₄; pH = 7; T = 70° C.; 24 hInhibition % Inhibitor 0.5 ppm 1 ppm 2 ppm 5 ppm 10 ppm Example 4 10 1090 100 100 DTPMP 10 22 75 95 100

Example 8

This example relates to CaSO₄ threshold effect at pH=7; T=70° C.; 6800ppm of CaSO₄+6000 ppm of Ca⁺⁺.

Following the method described in example 4, a solution of CaSO₄ wasprepared starting from CaCl₂ and Na₂SO₄. The results obtained aresummarized in Table 4.

TABLE 4 Operating Conditions: 6800 ppm CaSO₄ + 6000 ppm di Ca⁺⁺; pH = 7;T = 70° C.; 24 h Inhibition % Inhibitor 2 ppm 5 ppm 10 ppm Example 4 1591 99 DTPMP 22 45 96

Example 9

This example relates to CaSO₄ threshold effect at pH=7; T=90° C.; 6800ppm of CaSO₄.

Following the method described in example 5, a solution of CaSO₄ wasprepared starting from CaCl₂ and Na₂SO₄. The results obtained aresummarized in Table 5.

TABLE 5 Operating Conditions: 6800 ppm CaSO₄; pH = 7; T = 90° C.; 24 hInhibition % Inhibitor 0.5 ppm 1 ppm 2 ppm 5 ppm 10 ppm Example 4 0 5 1885 99 DTPMP 0 0 5 73 90

Example 10

This example relates to CaSO₄ threshold effect at pH=7; T=90° C.; 6800ppm of CaSO₄+6000 ppm of Ca⁺⁺.

Following the method described in example 5, a solution of CaSO₄ wasprepared starting from CaCl₂ and Na₂SO₄. The results obtained aresummarized in Table 6.

TABLE 6 Operating Conditions: 6800 ppm CaSO₄ + 6000 ppm di Ca⁺⁺; pH = 7;T = 90° C.; 24 h Inhibition % Inhibitor 0.5 ppm 1 ppm 2 ppm 5 ppm 10 ppmExample 4 10 15 18 91 99 DTPMP 0 0 8 38 45

Example 11

This example relates to calcium-sensitivity. The Grace “CLOUD POINTTEST” was used for testing the calcium-sensitivity. This simple methodallows calcium-sensitivity to be verified visually by estimating theturbidity point of an inhibitor solution in a concentrated calciumsolution. The inhibitor is added at increasing amounts to hard waterhaving the following characteristics: 500 ppm of Ca⁺⁺ (as CaCl₂), pH=8.3(0.05 M of boric buffer), at a temperature of 60° C. and 100° C. for 24h.

The turbidity of solutions after 24 hours was observed. The observationconfirmed that the turbidity is greater at increasing amounts ofinhibitor. The results obtained are summarized in Tables 7 and 8.

TABLE 7 500 ppm CaCO₃; pH = 8.3; T = 60° C. Inhibitor Dose Inhibitor 10ppm 30 ppm 50 ppm 100 ppm Example 4 clear clear clear clear ATMP clearturbid precipitate precipitate

TABLE 8 500 ppm CaCO₃; pH = 8.3; T = 100° C. Inhibitor Dose Inhibitor 10ppm 30 ppm 50 ppm 100 ppm Example 4 clear clear clear clear AMTPprecipitate precipitate precipitate precipitate

Example 12

This example relates to Fe³⁺ sequestering. The measurement of thesequestering power of iron is difficult both for traditionalphosphonates and for the polyaminomethylenephosphonate derivativesaccording to the present embodiment, because both products haveconsiderable dispersing ability, and if we considerer the colloidalaspect of the ferric hydrate, it is clear how difficult it could be todistinguish between the dispersed iron and the iron effectivelysequestered. It is well known that a very fine dispersion is verysimilar to a solution. It must be said that often, in practicalapplications, an effective dispersion is as useful as a truesequestration.

The method involves the addition of a known quantity of solution offerric ions to an aqueous solution of inhibitor at constant pH. After 24hours under agitation, the aspect of the sample is evaluated. Thesamples where a precipitate is present after 24 hours of agitation wereconsidered “precipitated,” and so the first clear sample was consideredin order to attribute a sequestring value. The results obtained aresummarised in Table 9.

TABLE 9 Fe³⁺ sequestering power expressed as mg Fe³⁺/g of productInhibitor pH = 5 pH = 6 pH = 7 pH = 8 pH = 9 pH = 10 pH = 11 pH = 12Example 4 0 60 180 200 260 360 200 20 HEDP 240 280 320 360 800 800 12001200 ATMP 40 60 100 120 140 180 120 0 DTPMP 40 60 80 140 220 130 60 20

The above data should be carefully evaluated, because the methodutilized does not allow a dispersion to be distinguished from a truechelation. However, an internal comparison indicated that traditionalphosphonates and the derivatives object of the present invention wereequally effective in the control of ferric ion.

The present invention further addresses the problem of corrosioninhibition.

The corrosion of metal equipment is an almost universal problem foraqueous systems. Two distinct areas coexist on a metal surface, an anodeand a cathode, which may be situated very close to each other and set upan electrical circuit with consequent Redox reactions leading to thesolubilization of the metals. MOre particularly, iron surfaces aretransformed into water-soluble Fe^(2+/3+) ions. The corrosion, andtherefore the loss of metal from part of the structure, takes place onlyin the anodic zone.

Without entering into the detail of the corrosion phenomenon, it isclear, however, that the damage caused by corrosive phenomena can beconsiderable in extent. Various methodologies and various products havebeen developed over time to address the problems related to the entityand various origins of corrosive phenomena. One of the more widespreadmethodologies involves the use, in aqueous phase, of suitable “corrosioninhibitors”. These compounds may be organic or inorganic films orprotective barriers between the metal surface and the of corrosionmedium. Such a protective film can be developed by the following means:

a. Precipitation of an inhibitor onto the metal surface;

b. Passivation of the metal surface;

c. Adsorption of an inhibitor onto the metal surface through theelectronic lone pair a donor element (N, S, O, P).

Example 13

In the following example, a simple test is described for evaluating theefficiency of the compounds according to the present embodiment ascorrosion inhibitors. The operating conditions and the procedure used inthe test are indicated below:

Taking water with 30 French degrees of hardness, bringing it at pH=8.5with diluted NaOH and than adding the desired quantity of inhibitor;

Adding carefully cleaned and weighed steel coupons to the solution.

The test lasts 5 days with a constant airflow bubbled through thesolution.

After 5 days, weighing the test pieces and estimating the loss inweight.

The results obtained are summarised in the following table:

TABLE 10 Inhibitor % weight loss after 5 days Example 4 0.25 ATMP 0.45HEDP 0.3 Blank 0.7

1. A scale inhibitor comprising at least one polymethylenephosphate derivative having the following formula:

wherein n is an integer comprised between 2 and 15000, wherein M is a hydrogen or a cation, wherein R₁, R₂, and R₃ are each independently selected from the group consisting of, CH₂PO₃M₂, CH₂R₄, wherein R₄ is CHOHCH₃, CHOHCH₂Cl, or CHOHCH₂OH, (CH₂)_(m)SO₃M, wherein m is 3 or 4, and CH₂CH₂R₅, wherein R₅ is CONH₂, CHO, COOR₆, COOX, or CN, wherein R₆ is CH₃ or C₂H₅, and wherein X is an alkali metal or ammonium, and wherein at least one of R₁, R₂, and R₃ is not CH₂PO₃M₂.
 2. The scale inhibitor according to claim 1, wherein at least one of the CH₂PO₃M₂ moieties in a terminal position on the molecule is replaced by a moiety selected from the group consisting of CH₂R₄, (CH₂)_(m)SO₃M, and CH₂CH₂R₅.
 3. The scale inhibitor of claim 1, wherein the polyaminomethylenephosphonate derivative is produced by a process of phosphonomethylation of polyamine derivatives employing the Mannich reaction.
 4. The precipitation inhibitor according to claim 1, wherein M is an alkali metal or ammonium.
 5. A method for inhibiting scale formation in water, the method comprising the step of adding to the water a scale inhibitor comprising at least one polymethylenephosphonate derivative having the following formula:

wherein n is an integer comprised between 2 and 15000, wherein M is hydrogen or a cation, wherein R₁, R₂, and R₃ are each independently selected from the group consisting of, CH₂PO₃M₂, CH₂R₄, wherein R₄ is CHOHCH₃, CHOHCH₂Cl, or CHOHCH₂OH, (CH₂)_(m)SO₃M, wherein m is 3 or 4, and CH₂CH₂R₅, wherein R₅ is CONH₂, CHO, COOR₆, COOX, or CN, wherein R₆ is CH₃ or C₂H₅, and wherein X is a an alkali metal or ammonium, and wherein at least one of R₁, R₂, and R₃ is not CH₂PO₃M₂.
 6. The method according to claim 5, further comprising the step of precipitating the polymethylenephosphonate derivative on a metal surface in contact with the water, thereby preventing corrosion of the metal surface.
 7. A method for sequestering iron ions in a water system, the method comprising the step of providing the water in the water system with a scale inhibitor comprising at least one polymethylenephosphonate derivative having the following formula:

wherein n is an integer comprised between 2 and 15000, wherein M is hydrogen or a cation, wherein R₁, R₂, and R₃ are each independently selected from the group consisting of, CH₂PO₃M₂, CH₂R₄, wherein R₄ is CHOHCH₃, CHOHCH₂Cl, or CHOHCH₂OH, (CH₂)_(m)SO₃M, wherein m is 3 or 4, and CH₂CH₂R₅, wherein R₅ is CONH₂, CHO, COOR₆, COOX, or CN, wherein R₆ is CH₃ or C₂H₅, and wherein X is an alkali metal or ammonium, and wherein at least one of R₁, R₂, and R₃ is not CH₂PO₃M₂. 